1. Field of the Invention
The present invention is related to the measurement of blood flow from a centrifugal blood pump.
2. Description of the Prior Art
Centrifugal pumps have been used for many years to pump a wide variety of different fluid materials. In general, a centrifugal pump includes a pumping chamber with an inlet aligned with a rotational axis of the pump, an outlet adjacent the periphery of the pumping chamber and an impeller mounted within the pumping chamber for rotation about an axis. The impeller in such pumps can be mounted on a drive shaft which extends outside the pumping chamber to a rotational drive source, or the shaft can be mounted within the pumping chamber as a spindle about which the impeller rotates (i.e. rotatably driven by means other than the rotation of the shaft, such as a magnet drive arrangement). In either case, as the impeller is rotated, it imparts force and velocity to the fluid, thus pumping the fluid from the pump inlet to the pump outlet.
In recent years, centrifugal pumps have been used extensively for pumping blood. One example of a centrifugal blood pump is shown in our U.S. Pat. No. 4,589,822, which is assigned to the same assignee as the present application.
Because the flow produced by a centrifugal pump may be independent of the speed of rotation (RPM) of the centrifugal pump impeller, in prior art centrifugal blood pump systems, an independent flow measurement device has been used.
There are two centrifugal blood pumps currently available in the United States--one produced by Bio-Medicus and the other by the assignee of the present application. The Bio-Medicus system uses an electromagnetic flowmeter, while the system of the assignee of the present application uses a Doppler ultrasonic flowmeter. Both of these approaches require that an appropriate transducer be placed in or near the blood conduit tubing.
There is a continuing need for improved flow measurement method for use in centrifugal blood pump systems. In particular, there is a need for a flow measurement method which is insensitive to stray electromagnetic radiation (such as from electro-cautery equipment) and which requires no operator-placed transducer.